What's The Problem?Â Pages: 12

tvlunn on Tue June 14, 2011 12:24 PM

Hello ............... I'm new to the forum, but have a quick question for the experts out there!

I was recently married and have adopted a 2006 Jeep Liberty with a 2.8 liter diesel engine. The auto runs fine and has been well maintained. However, my wife states that about 2 years back the AC quit cooling as good as it used to. What she experienced was the air was a just little warmer than normal and couldn't quite keep up with the demand on hot days. She then took it to the dealership which added a small amount of freon, but she states that didn't seem to resolve the issue, but in her opinion, actually made matters worse.

This past weekend I discovered the auto was overcharged once I connected my set of manifold gauges. I evacuated the system, pulled a deep vacuum (down to 500 microns) and it held the vacuum for 30 full minutes with absolutely no sign of a leak. I then weighed in 1.12 lbs as required and voila, the car began cooling much better.

The next morning, after sitting overnight, we got in the auto and it like to run us out on the way to church. I didn't check the temp of the air output, but it was about where one would expect on a very warm morning. After getting out of church, once again we cut on the air, but although better than it was the day before I worked on it, the AC just couldn't seem to get the car where it should be. As before I worked on it, I could tell the AC was cycling ............ and too much in my opinion. The AC would cool for approximately 8 seconds and then the compressor would be off for approximately 10 seconds.

The next morning, after sitting overnight, everything works great once again, up until the auto had been driven for 15 miles or so. Then the AC seemed to want to begin the cycling scenario too much. I do realize the compressor is designed to cycle, but this one is way too much after a certain period of time. In the manner it cycles after sitting in the hot sun or after its been driven some will not allow sufficient cooling. So, I do know for a fact the freon level is dead on. Since I'm no expert, what is the next most obvious thing to look for .................. and thanks in advance!

TRB on Tue June 14, 2011 5:10 PM

May need to get some pressure readings when it's cycling. Rapid clutch cycling could be a sign of low refrigerant. Might also check the clutch gap. .35-.60mm.

tvlunn on Tue June 14, 2011 5:51 PM

Thanks for the reply. I'll try to get some readings this weekend while it's "acting up"

I did check the pressures right after weighing in the required 1.12 lbs. After about 7 minutes of running the compressor was still engaged about 80% of the time and the outlet temp was approximately 54 degrees (outside temp was approximately 80 degrees with about 55% humidity). When engaged, the pressure was steady at about 47 / 230 .............. I've got it documented, but to my recollection, this is very close!

Now, you mentioned it may be low in refrigerant. I pulled a vacuum down to 500 microns and it held for a full 30 minutes. Therefore, I'm confident I do not have a leak. And, as mentioned. I weighed in the exact required 1.12 lbs. Therefore, I believe we can rule out a leak or improper charge. Thanks so much!

All comments are welcomed. I'm still learning and reading all the information I can get my hand on. This is how I learn the best!

TRB on Tue June 14, 2011 6:57 PM

80 degrees ambient. Pressures should be in the range of 25-35 & 200-300 with a proper charge. Center vent should be close to 45 degrees.

iceman2555 on Tue June 14, 2011 8:31 PM

How did you determine the system was overcharged?Why not try a few basic test. First, insure that the system is fully charged. Measure the inlet and outlet temps of the evaporator. Place the vehicle is a heavy heat load, MAX AIR/HIGH BLOWER/DOORS OPEN/ENGINE AT IDLE SPEED. Allow the system to operate for app 5-7 minutes. Test the inlet and outlet temps of the evap....these temps should be the same or within 3-5 degrees of each other. Once the charge rate has been determine, measure the inlet and outlet temps of the condenser. An average temp drop should be app 25-28 degrees. Publish your findings.If the temp drop is excessive this would indicate a possible restriction within the condenser. If not mistaken this vehicle has the 'high side' service port located on the liquid line. The pressure at this point may not indicate a true condenser restriction. Measure the inlet temp of the condenser and transfer this information to a pressure/tech chart and one is able to determine the 'discharge' pressures of the system.

-------------------------The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government. Thomas Jefferson

tvlunn on Wed June 15, 2011 6:15 AM

"First, insure that the system is fully charged. Measure the inlet and outlet temps of the evaporator. Place the vehicle is a heavy heat load, MAX AIR/HIGH BLOWER/DOORS OPEN/ENGINE AT IDLE SPEED. Allow the system to operate for app 5-7 minutes. Test the inlet and outlet temps of the evap....these temps should be the same or within 3-5 degrees of each other. Once the charge rate has been determine, measure the inlet and outlet temps of the condenser. An average temp drop should be app 25-28 degrees."

First, let me admit I am definitely no expert. Second, I appreciate the comments and help. Third, I'm not looking to find fault in the "experts" advice ................. but, did I interpret your advice correctly or is it stated backwards????? As mentioned earlier, after sitting overnight and the first 20 miles or so of driving, the AC gets plenty cold. It is definitely running as one would expect during this period. The AC does cycle periodically as one would expect, but not so often that it's interrupting it's cooling ability. It's just when it has been run for a while or has sat out in a parking lot under extreme heat that it seems to begin the excessive "cycling" scenario. It should cycle as I am aware, but not every 8 or so seconds ............. surely can't adequately coo the auto like that.

How did I determine it was overcharged: After sitting overnight and before running the system or auto, I knew the pressures should be stabilized and read the same on both the low and high side. According to my chart, the pressures for that day should have read around 95 PSI. I had a reading of 130 PSI on both the high and low side. It definitely wasn't undercharged. Thanks again!

tomw on Wed June 15, 2011 11:01 AM

tvlunn, if you poke around and read some of the other posts, there are some systems that do not equalize the pressure throughout the system when turned off. I don't know if yours is one of them. Apparent from reading is that they have some sort of TXV that holds the pressure. That said, if you measured high pressure on both the low and hi side, then you have hi pressure, perhaps someone put 'something' into the system that has a higher vapor pressure than R134a, as the pressure at rest would be the same if it were undercharged or overcharged. The R134a will have a specific pressure at a specific temperature it will boil to a gas if the pressure is lower than its vapor pressure at a given temperature. If it were bastardized by some additive, who knows what resting pressure should be... If you put a can of R134a in the freezer, the pressure inside the can goes down significantly. If you store it in the sun, the pressure rises. In both cases, there would still be some liquid, assuming the can has not been emptied. The liquid evaporates to fill the container until it reaches its vapor pressure at that temperature. A can that has ~102psi at 102F will have ~32 psi at 32F if it were filled with R12 .. the numbers are NOT exact, but if you look at a P/T table, you can see that R12 will store quite nicely with low pressure in your home freezer [lots are ~0F, significantly lowering the pressure] In short, you cannot tell overcharge by reading the pressure of a resting system. A small amount of refrigerant will boil to a gas, and fill the system with gas until its pressure is reached, and will then stop expanding or boiling, just like the refrigerant in the 'can tap' containers.

In your case, I would suspect the LPCO is either malfunctioning or may need to be adjusted. Check at what pressure the compressor cuts off when it is cold, after first starting when it is functioning at its best, and then check the cutoff pressure after it has gotten its 'sun load' or been run for a while. I'd bet you find that the LPCO is getting lazy, and cutting the juice to the clutch a bit too soon after it warms up.tom

-------------------------simplificate and add lightness

mk378 on Wed June 15, 2011 11:19 AM

Static pressure higher than the saturation pressure expected from temperature means that the refrigerant is contaminated with air. Remove it and don't reuse unless you have a recycler machine that can remove air.

tvlunn on Wed June 15, 2011 11:28 AM

Thanks Tomw .............. excellent information and for helping me to better understand "things". As you can tell, I'm certainly no expert, but I do try to do things the correct way and I do try to understand what should or shouldn't be occurring. Your message was very helpful in clarifying some of my misconceptions.

Now, the low pressure cut off switch you mentioned has been in the back of my mind as being a problem. But, I was never sure enough of my intuition and I am certainly not one who likes to be tagged as a "parts changer". Here are a few questions for you (or anyone else for that matter):

1- I am assuming the switch located on the top of the accumulator is the LPCO switch??? (I do need to order the factory service manuals for her auto as well)2- I wasn't aware there was an adjustment for the LPCO - where is the adjustment located and what is the procedure???3- Once again, I'm assuming if I need to replace the LPCO, I will need to evacuate the system once again because removing the switch will allow all refrigerant to escape???4- I just had another thought & would like an opinion. If I picked a time when the AC seemed to be cycling way too much and simply unplugged the LPCO for a brief period, shouldn't I expect the AC to quit cycling if the LPCO was the real culprit??? (or would I need to jump the terminals on the switch to do the test?)

Hey, thanks so much ................. I enjoy learning new skills and more importantly I want to understand things better. You are all so very helpful.

PS: iceman2555 responded to one of my post. Did I misinterpret his message ............ his reasoning sounds backwards to me. But now, I'm doubting myself???

Edited: Wed June 15, 2011 at 11:53 AM by tvlunn

iceman2555 on Wed June 15, 2011 5:37 PM

Not too sure what was backwards about my post....the first factor that must be known prior to a successful diagnosis is to know that the system is fully charged. The inlet and outlet temps of the evap will indicate this. Pressures are not an indication of a fully charged system. The question of how it was determined the system was overcharged was never answered. The second temp test is for the operation of the condenser....knowing how the two heat exchangers are operating is valid step to determine exactly where the problem exist. Of course one can 'throw' parts at a vehicle to determine a possible problem....and the cost of a LPCO is minute.....so replace the unit...or why not determine if the system is fully charged, the components are fully operational and then test the LPCO....!!! Could be the part...or there could be a possible pressure problem that results in a possible refrigerant release (PRV) and thus the system now operates at a lower pressure (undercharged) and the LPCO operates as designed. Your time...your money....but one thing must be known for sure.....the system must be fully charged to complete any valid diagnosis. No1 diagnostic tool.....know it is FULL!!!

-------------------------The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government. Thomas Jefferson

tvlunn on Thu June 16, 2011 8:11 AM

Thanks iceman2555 for your reply and your time.

I feel confident the system is full. My reasoning is I pulled a deep vacuum for about an hour (down to 500 microns) and once the pump was shut off the system maintained the 500 micron level for a full 30 minutes. That assures me there is no leakage. I then weighed in 1.12 lbs of R-134a as required by the manufacturer. Therefore, I am sure the system is full.

The additional test you mentioned on the heat exchangers is where I felt something was stated backwards in your earlier reply ............. you mentioned:

1- Test the inlet and outlet temps of the evapft> ............ these temps should be the same or within 3-5 degrees of each other2- Once the charge rate has been determine, measure the inlet and outlet temps of the condenserft>. An average temp drop should be app 25-28 degrees

As mentioned, I do not want to be a "parts changer". So, I'm learning ............... and learning much, thanks to folks like you. I'm certainly not a professional, but I do like to maintain my own vehicles. With each new problem I encounter, I'm always learning something new ................ and I've learned much over the years, but still no expert.

iceman2555 on Thu June 16, 2011 7:04 PM

The first test....EVAP in and out is a method to insure a properly charged orifice tube system. NO1 for diagnosis of a performance issue is know that the system is fully charged. Also this outlet temp aids in determining the app evaporator temp....which can be compared to the vent temp.......the condenser test, NO2, indicates if there is a possible restriction within the condenser or if there is a possible condenser cooling issue. So you see, they are not backward....It is possible that the LPCO is truly not functioning properly.....the difference between a parts changer and a tech is that you may wish to spend the money on a part that may or may not have failed....sorta like a test with a 'known good part' or one can follow some basic diagnostic procedures and determine what the lack of cooling issue is. Most techs have several 'known good parts' as part of our stash.....we use them as a test and then install a new part if required. All to often a part that is purchased for 'testing' and then does not solve the problem is returned as 'defective' to the point of purchase....when in reality there is nothing wrong with the part....this action drives up the cost of parts for everyone. Personally would prefer to know what had failed thur a true diagnosis procedure and then install the correct parts.Do not take offense at the 'tone' of some of the responses...it is just quite frustrating to offer a method of testing or evaluating a problem and then be told that what we are suggesting is not correct or does not follow the chain of thought as the poster.....if it is your desire to change the LPCO...then go for it....let us know if this solves the issue.....for a we all learn new things each day....every time I open the hood....there is a learning experience....heck...seems like each day is a new learning experience....and what I learned today....was should have stayed in dental school.....would be retired....lots of cash....pay someone to repair my auto.....have clean hands.....get my nails done....ahh..forget that one....one must draw the line somewhere....but the idea of being retired with lots of cash does sound very nice...yep...very nice indeed.

-------------------------The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government. Thomas Jefferson

tvlunn on Fri June 17, 2011 6:13 AM

Thanks again iceman2555!

Nope ............ I'm not taking anything in a negative fashion, for I am the "dummy" here. If I knew it all, I certainly wouldn't need the help of the folks on this forum. So, thanks to everyone.

However, I am now very confused regarding the statement you made in your last post. You indicated the statement made earlier was not backwards. OK, I believe you. I've never checked the air across the condenser as stated and it does make sense to do this. I would never have believed one could expect a 25 - 28 degree drop across the condenser. I'll try to complete your recommended testing this weekend and followup with the results.

By the way, someone else had mentioned the adjustment on the LPCO may need some attention. Exactly where is the adjustment "screw" located? And. if I do remove the LPCO, surely all refrigerant will escape and I will need to vacuum and recharge ............... correct? And no, I don't have a recovery system. I only maintain my own vehicles and AC work is very seldom needed. Thanks so much!

bromodragonfly on Sun June 19, 2011 2:58 PM

I think what he meant was that the temperature difference of refrigerant could be 25-28 degrees, and not air in/air out. So you would be measuring temperature at the refrigerant inlet/outlet of the condenser. When he said excessive temperature drop was a symptom of a restriction in the condenser, this happens because a restriction would cause a pressure drop within the condenser - liquid will boil if the pressure is reduced, and become 'cool' as it does. Liquid should only be permitted to boil immediately after the orifice or TXV, anywhere else and it will reduce efficiency of your AC system.

The air temp AFTER it has blown across the condenser should be higher than entering air. The air blowing across the condenser removes heat from the refrigerant, allowing it to cool and change into a liquid (and hopefully subcooled) state.

Some low pressure switches are not adjustable - the spring may have lost its tension over time, and will just need to be replaced. Can't say for sure if you will lose the refrigerant charge - some switches come as two pieces, the bottom connects to the lines and contains the schrader and a particular thread or connection style.. and the top will contain the spring/diaphragm/whatever and the electronic switch. Mine happens to be a two piece switch, but the bottom contains all the mechanical components - allowing me to pull the top piece and jumper it, if I never need to trouble shoot electrical - but I would have to evacuate if I ever needed to replace the bottom half.

If you hook up your gauges while the system is running, you may be able to pinpoint when that switch is cutting power to the compressor clutch. And maybe you will be able to find some info on what the setpoint is supposed to be for that particular switch or your particular vehicle.

-------------------------There is no knowledge that is not power

mk378 on Sun June 19, 2011 3:44 PM

If it's cycling on the LPCO at 45 psi, the switch is beyond adjusting -- replace it. You can jump the switch to test if that's why it's cycling. Nearly all American CCOT systems have a shrader valve on the accumulator port under the switch, so you can R&R switch with the system charged.

tvlunn on Sun June 19, 2011 7:45 PM

Thanks Bromodragonfly and MK378!!

Very good and helpful information. I figured I had misunderstood something, but wasn't sure what. Thanks for the clarification!

I really like the idea of jumping the LPCO switch. That will work nicely and seems to be easily done. So, I am assumig this is a normally open switch and by jumping it I will make it a closed switch. Is this true?

Thanks again!

bromodragonfly on Sun June 19, 2011 8:05 PM

Yes, most are normally open and will close on rise of pressure, so jumping it will give the compressor indication that there is enough low-side pressure to run without risk of damage.

-------------------------There is no knowledge that is not power

tvlunn on Mon June 20, 2011 10:27 AM

Before I move to the next step, I do believe I am at the point I need a little more "education". Is there a post somewhere on this site that explains the type ac system we have in our 2006 Jeep and all of its components. I'm interested to see which switches actually have the capability of cycling the AC ............ if more than one is used. I'm aware of the LPCO switch, but are there others? I would like to eliminate all of the possibilties if it is actually a switch problem. Thanks!

The fact I was abe to pull a vacuum to 500 microns and the system held that level for a full 30 minutes when I cut off the pump assures me there is no leakage. And the fact I weighed in the exact 1.12 lbs as required assures me the charge is correct. I do realize I need to get some gauge readings when it is "acting up", which I haven't done yet .....hopefully this weekend. My gut says it's a switch issue, but I realize gut feelings aren't the proper method for fixing something .............. but, I'm stubborn. I can purchase the cycling switch at my nearby Jeep dealer for about $29.00 For that price, I do believe I will go ahead and pick one up ............. it certainly won't break the bank. However, I would like to know more about my particlular system in case that doesn't resolve the issue. At that point I will be better prepared to move forward.

Thanks for all of the help and I will post back my findings in hopes it will help someone else!

Edited: Mon June 20, 2011 at 11:56 AM by tvlunn

bromodragonfly on Mon June 20, 2011 5:48 PM

The first time I had to do AC work on my car, I phoned up the dealership and asked them for a parts diagram of my specific AC system. It included a diagram and a list of all components, including switches.

Most vehicles will rely on the low pressure switch for compressor cycling. HVAC/Refrigeration systems will usually rely on a low pressure switch or a thermostat in the cooled space.

I am not sure if certain systems use the high pressure cutout for compressor cycling. It seems unlikely - in my mind, the high pressure cutout is more of a safety. Plus, with variable displacement compressors, the head pressure may never rise to the HP setpoint under normal conditions. Low pressure will most likely be the cycle operator when the load drops.

Hook your gauges up before you buy anything. Maybe the low side is dropping too low and the switch is fine.

-------------------------There is no knowledge that is not power

tvlunn on Thu June 23, 2011 3:06 PM

The weekend is fast approaching and I'm looking forward to getting the AC issue resolved, but I have another question for the experts:

This may not apply to all vehicles, but for a 2006 Jeep Liberty, does the electric fan that's mounted in front of the condenser get switched on when (1) a pre-determined engine compartment temperature is reached OR (2) does it run anytime the AC compressor is engaged. I would think the fan is configured to run at all times the compressor is engaged, but would like to know for sure. I guess it's possible it could be either #1 or #2, but only want to know what should occur when the compressor is engaged. Thanks so much!

Edited: Thu June 23, 2011 at 3:11 PM by tvlunn

bromodragonfly on Thu June 23, 2011 5:56 PM

Typically, in regards to the AC system, the fan will engage when the high side reaches a certain pressure. I'd guess between 200-300psi.

But the fan will can also engage from other things such as engine coolant temp, transmission fluid temp, etc.

-------------------------There is no knowledge that is not power

tvlunn on Thu June 23, 2011 7:04 PM

Thanks Bromodrangonfly!!!!!!!!!!!!!!!!

That's good information .......... after my wife got home this afternoon, I checked the AC and fan operation. Sure enough, when I first started the auto and AC, I noticed the electric fan wasn't running. I told myself that wasn't good, but a short time later the fan did cut on. So, my theory that the fan should run anytime the compressor was engaged was incorrect. Your information is just in time to make me feel better and understand "things" a little better.

Today was a mild day in SC ............... about 84 degrees this afternoon. My wife stated the AC performed very well today and it also did well with the auto idling in the driveway while I made a few checks. I'm still leaning towards the LPCO switch as being the main issue with our problem .............. but I'm no expert. I did purchase a LPCO and will put it on this weekend. More later. Thanks again!!!!!!!!!!!!!!!!!!!!!!!!!

Edited: Thu June 23, 2011 at 7:53 PM by tvlunn

tvlunn on Mon June 27, 2011 11:23 AM

OK .................... all is well as of this writing. Saturday morning I replaced the LPCO switch and the AC has been performing much better. I drove the Jeep a litle Saturday morning after I replaced the switch and the air from the middle duct was measuring about 46 degrees with an outside temp of about 90 degrees. I was pleased with that.

We drove the Jeep on Sunday and it performed well once again. All suction lines are sweating and "making water" as one would expect and the compressor is staying engaged much longer before cycling. By golly, I think the problem is resolved. Thanks to everyone for helping ............. I certainly have more knowledge to add to my bag of tools because of you folks!